Please note that all steps have to be done on a linux PC with root access.

The flash can be used out of NanosG20's 2nd stage loader which is, in fact, a small Linux system. To enter this loader connect a serial terminal (115200 8N1) to the male DSUB9 connector, hold SW1 during power-up and choose "Drop to shell".

http://armbedded.eu/node/383 describes the process out of a running system from SD card. If you use the bootloader - which works well for this - some things are different:
1. UBI is already attached
2. /dev/ubictrl is named /dev/ubi_ctrl
3. The tar command cannot decompress gz or bz2 directly. Do the uncompress stage separately on your development system.
4. When mounting NFS over ethernet, you'll have to run udhcpc first.

Actually, there is no difference except the smaller size available on flash. Please keep in mind that data stored on NAND is being compressed (by the UBI FS layer). So, there might be more CPU load needed.